3,474 research outputs found
Adjoint rings are finitely generated
This paper proves finite generation of the log canonical ring without Mori
theory.Comment: completion of the project initiated in arXiv:0812.3046; v2,v3:
presentation improved, includes parts of arXiv:0707.4414 in Sections 4 and
Design an engaging interactive experience for people with dementia
The population of the world is increasing resulting in a higher number of people
dealing with dementia–whether being diagnosed with it or taking care of someone
that is diagnosed with it. This master thesis aims to investigate which types of
multi-media technology-based experiences can improve the quality of life for people
with dementia.
To reach the goal of the thesis–investigation will be done through different iterations
of a design method; divergence, transformation and convergence. These iterations
will include observations, interviews and using personas as a tool to design.
The results from the methods were used to create a high fidelity prototype which
was evaluated by an expert in the field of dementia
Using causal models to distinguish between neurogenesis-dependent and -independent effects on behaviour
There has been a substantial amount of research on the relationship between hippocampal neurogenesis and behaviour over the past fifteen years, but the causal role that new neurons have on cognitive and affective behavioural tasks is still far from clear. This is partly due to the difficulty of manipulating levels of neurogenesis without inducing off-target effects, which might also influence behaviour. In addition, the analytical methods typically used do not directly test whether neurogenesis mediates the effect of an intervention on behaviour. Previous studies may have incorrectly attributed changes in behavioural performance to neurogenesis because the role of known (or unknown) neurogenesis-independent mechanisms were not formally taken into consideration during the analysis. Causal models can tease apart complex causal relationships and were used to demonstrate that the effect of exercise on pattern separation is via neurogenesis-independent mechanisms. Many studies in the neurogenesis literature would benefit from the use of statistical methods that can separate neurogenesis-dependent from neurogenesis-independent effects on behaviour
Pseudoreplication invalidates the results of many neuroscientific studies
Background: Pseudoreplication occurs when observations are not statistically independent, but treated as if they are. This can occur when there are multiple observations on the same subjects, when samples are nested or hierarchically organised, or when measurements are correlated in time or space. Analysis of such data without taking these dependencies into account can lead to meaningless results, and examples can easily be found in the neuroscience literature.\ud
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Results: A single issue of Nature Neuroscience provided a number of examples and is used as a case study to highlight how pseudoreplication arises in neuroscientific studies, why the analyses in these papers are incorrect, and appropriate analytical methods are provided. 12% of papers had pseudoreplication and a further 36% were suspected of having pseudoreplication, but it was not possible to determine for certain because insufficient information about the analysis was provided.\ud
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Conclusions: Pseudoreplication undermines the conclusions from statistical analysis of data, and it would be easier to detect if the sample size, degrees of freedom, the test statistic, and precise p-values are reported. This information should be a requirement for all publications
Wait-Free Solvability of Equality Negation Tasks
We introduce a family of tasks for n processes, as a generalization of the two process equality negation task of Lo and Hadzilacos (SICOMP 2000). Each process starts the computation with a private input value taken from a finite set of possible inputs. After communicating with the other processes using immediate snapshots, the process must decide on a binary output value, 0 or 1. The specification of the task is the following: in an execution, if the set of input values is large enough, the processes should agree on the same output; if the set of inputs is small enough, the processes should disagree; and in-between these two cases, any output is allowed. Formally, this specification depends on two threshold parameters k and l, with k<l, indicating when the cardinality of the set of inputs becomes "small" or "large", respectively. We study the solvability of this task depending on those two parameters. First, we show that the task is solvable whenever k+2 <= l. For the remaining cases (l = k+1), we use various combinatorial topology techniques to obtain two impossibility results: the task is unsolvable if either k <= n/2 or n-k is odd. The remaining cases are still open
Succinct progress measures for solving parity games
The recent breakthrough paper by Calude et al. has given the first algorithm
for solving parity games in quasi-polynomial time, where previously the best
algorithms were mildly subexponential. We devise an alternative
quasi-polynomial time algorithm based on progress measures, which allows us to
reduce the space required from quasi-polynomial to nearly linear. Our key
technical tools are a novel concept of ordered tree coding, and a succinct tree
coding result that we prove using bounded adaptive multi-counters, both of
which are interesting in their own right
KReach : a tool for reachability in petri nets
We present KReach, a tool for deciding reachability in general Petri nets. The tool is a full implementation of Kosaraju’s original 1982 decision procedure for reachability in VASS. We believe this to be the first implementation of its kind. We include a comprehensive suite of libraries for development with Vector Addition Systems (with States) in the Haskell programming language. KReach serves as a practical tool, and acts as an effective teaching aid for the theory behind the algorithm. Preliminary tests suggest that there are some classes of Petri nets for which we can quickly show unreachability. In particular, using KReach for coverability problems, by reduction to reachability, is competitive even against state-of-the-art coverability checkers
Vitrification in a 2D Ising model with mobile bonds
A bond-disordered two-dimensional Ising model is used to simulate Kauzmann's
mechanism of vitrification in liquids, by a Glauber Monte Carlo simulation. The
rearrangement of configurations is achieved by allowing impurity bonds to hop
to nearest neighbors at the same rate as the spins flip. For slow cooling, the
theoretical minimum energy configuration is approached, characterized by an
amorphous distribution of locally optimally arranged impurity bonds. Rapid
cooling to low temperatures regularly finds bond configurations of higher
energy, which are both a priori rare and severely restrictive to spin movement,
providing a simple realization of kinetic vitrification. A supercooled liquid
regime is also found, and characterized by a change in sign of the field
derivative of the spin-glass susceptibility at a finite temperature.Comment: Final version, as accepted in EPJ B, reformatted to 9 pages,
otherwise minor rephrasing, 10 figure
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